The demands include Doha ending support for the Muslim Brotherhood and closing broadcaster Al-Jazeera.

Saudi Arabia and its allies have not said what steps they could take next, but there are fears of a wider embargo that would hurt the Qatari economy, with credit ratings agency Moody's announcing it was changing Qatar's outlook to negative over the crisis.

13 demands

The countries issued the 13-point list of demands on June 22, giving Qatar 10 days to respond.

The deadline was extended by 48 hours on Sunday at the request of Kuwait, which is mediating in the crisis, and Qatar handed in the response on Monday.

The contents of the response have not been disclosed, but Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman Al-Thani said the list of demands "is unrealistic and is not actionable".

Qatar has denied any support for extremism and accused the countries of seeking to infringe on its sovereignty.

The other demands include Qatar downgrading ties with Iran -- Saudi Arabia's regional arch-rival -- and shutting down a Turkish military base in the emirate.

In his phone call with Sisi, Trump "reiterated the need for all countries to follow through on their commitments at the Riyadh summit (in May) to stop terrorist financing and discredit extremist ideology," the White House said.

US Secretary of State Rex Tillerson spoke with the emir of Kuwait and stressed Washington's "support" for his efforts to mediate a solution to the crisis, Kuwait's KUNA news agency said.

The UN meanwhile said its under-secretary general for political affairs, Jeffrey Feltman, was in Kuwait for talks on ending the dispute.

Germany's Foreign Minister Sigmar Gabriel said in a statement that he was "pleased to see talks between (the US secretary of state) and the Kuwaitis".

"It is now a matter of the parties entering into negotiations," he added.

Qatar urges dialogue

Qatar has said repeatedly it is ready for talks on the crisis, and Sheikh Mohammed reiterated that on Wednesday.

The minister accused Saudi Arabia and its regional allies of "demanding that we must surrender our sovereignty as the price for ending the siege".

Riyadh and its supporters have severed air, sea and ground links with Qatar, cutting off vital routes for imports including food.

They also ordered Qatari citizens to leave their territories and took various steps against Qatari firms and financial institutions.

The crisis has raised concern of economic consequences as well as growing instability in the region, home to some of the world's largest energy exporters and key Western allies which host US military bases.

Energy-rich Qatar has been defiant throughout the crisis, insisting it can weather action taken against it.

On Tuesday it even announced a major boost in planned natural gas output, with Qatar Petroleum saying it would increase production to 100 million tonnes a year by 2024, up 30 percent from current levels.

Qatar is the world's leading producer of liquefied natural gas.

Its energy riches have transformed Qatar into one of the world's wealthiest countries, a major international investor and a regional player that will host the 2022 football World Cup.